The long-range purpose of the project is to study the biochemistry, morphology, pharmacology and physiology of inner ear neurons and other cells and to describe the mechanisms of their interactions. 1. Enkephalin-like immunoreactivity using the PAP-technique has been demonstrated in efferent synapses on outer hair cells in the guinea pig cochlea at the ultrastructural level. Biochemical studies to identify the opiate(s) in the cochlea are in progress, using high-performance liquid chromatography (HPLC) and radio immunoassay (RIA) techniques. Biochemical opiate receptor studies on the cochlea are in progress. 2. Cells of origin of olivocochlear neurons have been shown to both contain acetylcholinesterase and to exhibit enkephalin-like immunoreactivity. 3. Aspartate aminotransferase (AAT) - and glutaminase-like immunoreactivity at a high level has been found in spiral ganglion cells and at synapses in the organ of Corti.